This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.High-quality prostate images were obtained with transceiverarrays at 7T after performing subject-dependent local transmitB1 (B1 ) shimming to minimize B1 losses resulting from destructiveinterferences. B1 shimming was performed by alteringthe input phase of individual RF channels based on relativeB1 phase maps rapidly obtained in vivo for each channel of aneight-element stripline coil. The relative transmit phasesneeded to maximize B1 coherence within a limited regionaround the prostate greatly differed from those dictated by coilgeometry and were highly subject-dependent. A set of transmitphases determined by B1 shimming provided a gain in transmitefficiency of 4.2 2.7 in the prostate when compared to thestandard transmit phases determined by coil geometry. Thisincreased efficiency resulted in large reductions in required RFpower for a given flip angle in the prostate which, when accountedfor in modeling studies, resulted in significant reductionsof local specific absorption rates. Additionally, B1 shimmingdecreased B1 nonuniformity within the prostate from(24 9%) to (5 4%). This study demonstrates the tremendousimpact of fast local B1 phase shimming on ultrahigh magneticfield body imaging.
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